A) Field of Invention
The present invention relates to a variable posture work chair with a displaceable armrest assembly which maintains a constant user defined spatial relationship to a moveable seat pan and backrest.
B) Known Art
The proliferation of computer terminals at the modern workstation has spawned a variety of attempts to provide a more comfortable environment for seated workers. The general discomfort that afflicts the legs, lower back, neck, shoulders and wrists of seated workers can be partially offset by building better seating devices, particularly those that conveniently allow a wide range of posture changes. An in depth discussion of the advantages and disadvantages of various seating designs is contained in my previous patent.
The builders of work chairs face several key challenges in effecting their designs. Among the most important:
Comfort and utility. A work chair must be adaptable to a wide range of work place requirements while maintaining ergonomically correct comfort for a seated user.
Ease of use. A seated user should be able to transition smoothly from one position to another with a minimum of mechanical intervention. The most efficient way of achieving this is by building a chair mechanism that effects its changes through a controllable rocking movement.
Adjustability. A single design platform should be able to accommodate a wide range of human body sizes while easily adapting to the changing needs of the workplace.
Integration of components and their movements. Interconnecting a moveable seat pan, backrest and armrest assembly so that they function in a synergistic fashion while effecting utilitarian variable posture remains a key focus of invention in the field of work chair design.
Engineering and production costs. A design must be relatively simple to engineer and cost effective to build, or it stands no chance of succeeding in the marketplace.
In addition much design emphasis is now being placed on the aforementioned term "variable posture", and while the term is important in the ergonomic sense it lacks any mechanical definition. A simple way to measure the degree of variable posture in any chair design is to assess the useable range of seat pan tilt the design provides. The greater the range of useable tilt (up to a maximum) the greater the shift in body footprint and center of gravity, this being variable posture. By "useable" is here meant that a seated user should be able to tilt the seat pan to a chosen inclination/declination from the horizontal, lock that inclination/declination in place and work comfortably from that position for extended periods of time. Obviously, for this scenario to succeed the other elements of the chair design must function in harmony with the movement of the seat pan.
A detailed discussion of the variable posture issue and several relevant patented designs is contained in my aforementioned patent. Further, U.S. Pat. Nos. 5,577,802 to Cowan and Kmicikiewicz and 5,540,481 to Roossien et al show chair designs which attempt to effect easy adaptation to the movements of a seated user. While Cowan shows armrests they are not crucial to the central design; for Roosien et al the armrests are superfluous. U.S. Pat. No. 5,536,070 to Lemmen shows an ergonomic armrest assembly but attempts no real integration with the seat pan and backrest. U.S. Pat. No. 4,277,102 to Aaras et al describes a chair with individually supported armrests. Various armrest assemblies are described in U.S. Pat. Nos. 5,439,267 to Peterson et al, 5,407,249 to Bonutti, 5,393,124 to Neil, 5,380,065 to Rohrer, 5,369,805 to Bergsten et al, 5,366,276 to Hobson et al, 5,215,282 to Bonutti, 5,056,863 to DeKraker et al, 5,009,467 to McCoy, and 4,887,866 to Rusin.
Several observations come to light when examining the prior art in this field. First, and in general, when chair designers attempt to build a relationship between a seat pan and a backrest they fail to adequately integrate armrest assemblies into their designs. Even when the appearance of attention to detail is given, armrest assemblies are usually dispensable add-ons to the basic chair assembly. Conversely, the designers of armrest assemblies show little interest in integrating the functions of their designs with the movements of a variable posture seat pan and backrest. Armrests, whether built individually or interconnected on a frame, are designed to be added onto, and not integrated into, a pre-existing chair.
More specifically, current design practice almost always fixedly attaches armrest assemblies to a tiltable seat pan or its mount without adequately separating and then integrating the functions of the two assemblies. If one posits that the chief a function of a work chair armrest assembly is to align a user's forearms with a keyboard or other work surface it can be seen that this alignment is constantly being upset by the movements of the seat pan to which it is locked, movements which are necessary to effect variable posture. Further, if one attempts to lock the armrests into an aligned position the seat pan can only follow, thus affording a position which may not be the most comfortable for the user's needs.
It is to the aforementioned issues that the substance of the current invention is therefore addressed.
Objects and Advantages
The objects and advantages of my previous patent are incorporated into the present invention.
Further, it is the general objective of the present invention to provide a variable posture chair assembly that integrates and synchronizes the functions and movements of a seat pan, a backrest, two armrests and, optionally, a leg-rest for a seated user. The chair will be adaptable to a wide variety of workplace requirements, comfortable in all positions, easy to use, adjust to varying body sizes and be relatively simple and cost effective to build.
Specifically
A significant advantage of the present invention is its implementation of a compound lever mounting assembly to effect a differential in tilt among an armrest assembly, a seat pan and a backrest. A seated user will enjoy several key benefits by effecting this differential tilt. Chief among these is the ability to vary the angle of the seat pan and backrest to the maximum practical extent while simultaneously keeping the armrests, and thus the forearms, aligned with a work surface such as a keyboard. Only a rocking motion and operation of a braking assembly are necessary to effect basic changes in alignment. Simple controls allow further manual adjustments that remain part of the configuration.
The compound lever mounting assembly consists in part of two upper and two lower side rails that act as two levers mounted to a central dual fulcrum. Other elements of the chair are a seat pan assembly, a backrest assembly, an armrest assembly and an appropriate base. Elements may be linked to one or both of the levers. The key functions of the assembly are summed up as follows and are detailed later in the specification:
Two upper and two lower side rails are connected by a plurality of axes so that the four tilt in tandem as one upper and one lower lever. The levers are mounted to a dual fulcrum positioned near their center; the fulcrum may be moved to the forward end of the lever assembly. A seat pan assembly is attached to one end of the lever assembly and the armrest and backrest assemblies are attached to the other. The lever assembly may rock freely or be locked down; its total range of tilt is herein referred to as "tilt range".
The dual axles of the seat pan mount are connected to the forward end of the compound lever so that the axles share the same constant vertical axis as that of the non-moving central dual fulcrum. The seat pan itself is hinged to the upper of the two axles and is loaded by a spring at a constant forward inclination that changes only when counter loaded by a seated user. The maximum range of seat pan tilt is herein shown to be 33-40 degrees. A forward stop and the available rearward tilt of the compound lever assembly limit this range. It is anticipated that most users of the chair will find approximately 18 degrees of loaded seat pan tilt and 15 degrees of free tilt to be adequate for daily use.
The armrest assembly is also referenced by the two levers to the non-moving vertical axis of the central dual fulcrum. The vertical axis of the armrest assembly mount may be referenced in the same fashion as that of the seat pan or it may be offset. offsetting the mount is the preferred embodiment of the present invention. The degree of armrest assembly fore-aft tilt created by the interaction of its mount with the compound lever is herein referred to as "linked tilt range". This range will be shown to be variable depending upon the method of mounting the armrest assembly to the lever assembly. The fore-aft tilt of the armrest assembly may also be manually adjusted, herein referred to as "positional displacement".
The adjustable backrest assembly is referenced to the upper of the two levers only. It tilts in tandem with a single, not a dual lever. Thus the variable movements of the backrest are synchronized with the tilt of the loaded seat pan.
The difference in the default range of tilt between the lever assembly and the armrest assembly is determined by subtracting the linked tilt range from the tilt range. The difference is herein referred to as "differential tilt". The differential tilt of the assembly is determined by the method of attaching the armrest assembly to the compound levers and the degree of tilt range.
This assembly allows a seated user to precisely align his or her forearms with a keyboard or other work surface while simultaneously adjusting the angle of the seat pan and lock that alignment into position. Necessary height compensations can be achieved through central chair height adjustment, the armrests themselves or the use of a detached adjustable keyboard desk. If a desk assembly is mounted directly to the armrest assembly no height compensation is needed. Further, a user may set the horizontal tilt of the armrest assembly to satisfy a specific need; this preset (positional displacement) determines a resulting default range of armrest movement. If the user locks the mounting assembly into a specific position the armrests remain at a solidly fixed position while the user enters into and exits from the chair and the seat pan continues to tilt over its available range of movement. This facilitates entering into or exiting from a seated position, particularly one of reclining. The user can also effect a rocking and stretching motion consistent with variable posture, this because the seat pan and backrest are pivotally fixed to their mounts.
A further significant advantage of the present invention is the use of a single integrated armrest assembly to be used in conjunction with a seat pan, a backrest, and, optionally, a leg-rest. This assembly has the following advantages:
It synchronizes easy user effected lateral adjustment of two armrests from a single control, thereby accommodating a wide range of shoulder widths.
It synchronizes easy user effected fore and aft tilt of two armrests from a single control by mounting the assembly so that it pivots controllably on its long axis within the mounting frame.
It allows for simple height and horizontal adjustment of the armrests.
It is relatively easy to engineer and cost effective to build.
The advantages of using a keyboard desk or an abdominal rest when attached to an armrest assembly were thoroughly covered in my previous patent. The present design incorporates these advantages and facilitates the use of these accessories by providing for easy mounting to and removal from the assembly.
Further objects and advantages of the present invention will become apparent from a consideration of the drawings and ensuing description.